Evidence for complex formation

So far, we have presented evidence for direct reaction mechanisms and shown that various dynamic aspects of reactions can be interpreted in terms of these mechanisms. From what has been described in the previous sections and other related experiments, we see that the stripping mechanism is rather widespread, if not universal. 

However, it should be noted that the dynamic studies of ion—molecule reactions have always been carried out in an energy range of a few eV or a few 10 eV. Even the lowest energy at which dynamics has been studied, 

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While there is clear evidence for complex formation between certain electron donor and electron acceptor monomers, the evidence for participation of such complexes in copolymerization is often less compelling. One of the most studied systems is S-.V1 Al I copolymerization/8 75 However, the models have been applied to many copolymerizations of donor-acceptor pairs. Acceptor monomers have substituents such as carboxy, anhydride, ester, amide, imide or nitrile on the double bond. Donor monomers have substituents such as alkyl, vinyl, aryl, ether, sulfide and silane. A partial list of donor and acceptor monomers is provided in Table 7.6.65.-... 

Equilibrium constants for complex formation (A") have been measured for many donor-acceptor pairs. Donor-acceptor interaction can lead to formation of highly colored charge-transfer complexes and the appearance of new absorption bands in the UV-visible spectrum may be observed. More often spectroscopic evidence for complex formation takes the font) of small chemical shift differences in NMR spectra or shifts in the positions of the UV absorption maxima. In analyzing these systems it is important to take into account that some solvents might also interact with donor or acceptor monomers. 

Exactly the same problem arises with the recent studies of NiO solubility by Tremaine and Leblanc (25) and again the thermodynamic data on the aqueous anionic species at 300 C are likely to be more reliable than on the Ni + ion. There is good spectroscopic evidence for complex formation in chlorides of nickel (II), (26) cobalt (II) (27), and copper (II) (28) at 300°C and above. Most of the work was done at rather high Cl concentrations but qualitatively the effects of dielectric constant and concentration are as expected. A noteworthy feature (which estimation procedures will have to allow for) is the change from 6 to 4 coordination at the lower pressures (150-300 bar) and the higher Cl concentrations. This change appears to take place with only 2 or 3 Cl ions coordinated to the metal (at least in the case of Ni(II)). 

It can be shown that the virial type of activity coefficient equations and the ionic pairing model are equivalent, provided that the ionic pairing is weak. In these cases, it is in general difficult to distinguish between complex formation and activity coefficient variations unless independent experimental evidence for complex formation is available, e.g., from spectroscopic data, as is the case for the weak uranium(VI) chloride complexes. It should be noted that the ion interaction coefficients evaluated and tabulated by Cia-vatta [10] were obtained from experimental mean activity coefficient data without taking into account complex formation. However, it is known that many of the metal ions listed by Ciavatta form weak complexes with chloride and nitrate ions. This fact is reflected by ion interaction coefficients that are smaller than those for the noncomplexing perchlorate ion (see Table 6.3). This review takes chloride and nitrate complex formation into account when these ions are part of the ionic medium and uses the value of the ion interaction coefficient (m +,cio4) for (M +,ci ) (m +,noj)- Io... 

The presence of either HEDTA or EDTA resulted in significantly lower neptunium and plutonium sorption. Complexation of the neptunium and plutonium by HEDTA and EDTA may have caused the reduced sorption. However, this evidence for complex formation was not consistent with the observations made in the solubility studies (HEDTA increased and EDTA decreased neptunium solubility neither affected plutonium solubility). Thus, HEDTA and EDTA may have decreased neptunium and plutonium sorption through some undetermined effect on the sediment minerals. 

Since there is no evidence for complex formation between alkyl halides (H=R) and unsaturated compounds, reaction c is rather unlikely when alkyl halides are used as cocatalysts. Alkyl chloride cocatalysts in cationic polymerizations were postulated by Pepper (86,87) and corroborated experimentally (88). 

While our results indicate clearly an interaction between Al2Me6 and methyl chloride, we do not have direct evidence for complex formation. Evidently if a complex such as Al2Me6-MeCl exists at all, its concentration must be very low. It was theorized that chances to find evidence for the existence of a complex between a trialkylaluminum and methyl chloride would be more successful by using a monomeric trialkylaluminum, such as Al-i-Bu. Experiments with the Al-i-Bu -MeCl system are discussed below. 

These results are considered to be strong evidence for complex formation between AliBu3 and MeCl. 

Krot A. N., Hutcheon I. D., and Keil K. (2002c) Anorthite-rich chondrules in the reduced CV chondrites evidence for complex formation history and genetic links between CAIs and ferromagnesian chondrules. Meteorit. Planet. Sci. 37, 155-182. 

Another ligand, 2-(2-pyridyl)-imidazoline, exhibited the Pfeiffer effect in water. The effect was observed with zinc(II) as the central metal ion and d-a-bromocamphor-TT-sulfonate as the optically active environment. However, the effect was not observed for this ligand and nickel(II) in water, but the evidence for complex formation was not conclusive in this case. 

There is evidence for complex formation of a coumarin derivative with magnesium ions... 

The substitution reaction of cyanide with benzyl bromide (Table 1) was evaluated with and without silacrown promoted catalysis and compared with 18-crown-6 and decamethylcyclopentasiloxane (Dj). Reaction conditions and times were not optimized. The catalytic activity of the sila-17-crown-6 appeared to be equivalent to 18-crown-6. Dodecamethylcyclopentasiloxane did not demonstrate catalytic activity. The specificity of the sila-14-crown-5 for sodium ions and not potassium ions provides evidence for complex formation analogous to the crown ethers. 

The two earliest reports of the COClj-BFj system are apparently contradictory the earlier [738a] claims that phosgene and boron(III) fluoride interact to form compounds (but does not identify these in any way), the later [1329] suggests that phosgene and boron(III) fluoride do not form a complex, even at temperatures as low as -120 C. However, a more detailed investigation [1329] resolved these anomalies. The phase diagram for the COClj-BFj system is illustrated in Fig. 9.1, and shows clear evidence for complex formation at compositions BF3.COCIJ (m.pt. -134.3 C) and BF3.2COCIJ (m.pt. -137.0 C) [1329]. 

An equimolar solution of silicon(IV) chloride and phosgene in tetrachloromethane showed no evidence for complex formation, as monitored by infrared spectroscopy [ICIl]. Indeed, i.r. spectroscopy has been used to determine phosgene levels in commercial SiCl ... 

Molybdenum(V) chloride is reasonably soluble in liquid phosgene at 0 C, whereas tungsten(VI) chloride is only sparingly soluble. The results of the tensimetric titrations of molybdenum(V) chloride and tungsten(VI) chloride with phosgene at 0 C are presented in Fig. 9.8 [376] there is no evidence for complex formation. 

Iron(in) chloride is a common impurity in commercial phosgene at the 0.08-0.2% level [1168]. Attempts to isolate an adduct between phosgene and iron(Ill) chloride were unsuccessful [1012], and a tensimetric titration of ruthenium(IIl) chloride with phosgene showed no evidence for complex formation [ICIl]. 

Another supporting evidence for complex formation as a prerequisite to synergism was obtained from the study of the catalysis of phenyl isocyanate-butanol reaction by soluble organic cobalt compounds in presence and absence of DABCO catalyst. The results obtained are presented in Figures 4 and 5. It is evident that the combination of DABCO catalyst with divalent cobalt compounds shows synergistic effects while the trivalent cobalt acetylacetonate shows relatively low activity. The explanation of these observations is the structure of these compounds. 

Horman I., Carpenter R.A., Brambilla E. and Dreux B. (1981) Evidence for complex formation between thiamine and the chlorogenatc ion in aqueous solution. 9th. Int. Colloq. Chem. Coffee (London, 16-20.6.1980) (ASIC, 1981), 99-106. 

F. Power, T. Kozik, M. Interaction of Carbon Dioxide with Transition-Metal-Substituted Heteropolyanions in Nonpolar Solvents. Spectroscopic Evidence for Complex Formation, Inorg. Chem. 1998, 37, 4344. 

Katsoulis, D. E. Taush, V. S. Pope, M. T., Interaction of Sulfur Dioxide with Heteropolyanions in Nonpolar Solvents. Evidence for Complex Formation, Inorg. Chem. 1987, 26, 215. (d) Katsoulis, D. E Pope, M. T. Reactions of Heteropolyanions in Non-Polar Solvents. 3. Activation of Dioxygen by Manganese(ll) Centers in Polytungstates - Oxidation of Hindered Phenols,/. Chem. Soc. Dalton Trans. 1989, 1483. 

Another kind of indirect evidence for complex formation is found in the study of collision-induced dissociation of D3 by Leventhal and Friedman [135]. They found in tandem mass spectrometer experiments that the energy threshold (CM) of the reaction D3 -hX- D + D2 + Xis independent of X, where X = He, He, and Ne. This means the whole of the energy available to drive the reaction (= CM energy) is always used. Some sort of XD3 complex would be necessary for this complete energy transfer. 

Herman et al. [140] then obtained decisive evidence for complex formation in their crossed beam experiments, described above, in which both velocity and angular spectra were measured. In the reaction... 

Experimental studies on the hydrolysis of the Th" ion, its complexes with strong inorganic hgands, and the solubility of thorium oxides or hydroxides ate usually performed with low concentrations of thorium in perchlorate, chloride, and nitrate media. There is no evidence for complex formation between Th" and CIO4 however, chloride and nitrate form weak Th(lV) complexes as discussed in Sections Vlll.2.2.1 and X. 1.3.3, respectively. For the evaluation of equihbrium constants at zero ionic strength from data in chloride and nitrate media we have therefore the general problem to decide if the activity of Th", , should be calculated using a... 

Perchlorate, chloride and nitrate are the anions in the ionic media commonly used to investigate the hydrolysis of Th(IV). There is no evidence for complex formation between Th" and CIO. Chloride and nitrate complexes are discussed in Sections VIIt.2.2.1 and X.1.3.3, respectively. Hence, it is necessary to discuss if and how these will affect the reported equihbrium constants for the Th(IV) hydroxide complexes. As discussed in Sections Vin.2.2.1 and X.1.3.3, the experimental data in the binary Th(IV) chloride and nitrate systems can be described with similar accuracy using both complexation and ion interaction models. When evalrrating the hydrolysis data in chloride and rritrate iorric media, this review has used the ion interaction model with the interaction coefficients s(Th", Cl ) = (0.25 + 0.03) kg-mol and 8(Th", NOj) = (0.31 + 0.12) kg mol, respectively. With this model no correction for the formation of thorirrm chloride and rritrate complexes is necessary (see Section VI.3). 

Figure 3. Spectral evidence for complex formation between CuCl and NBD in ethanol ( ll)...

They developed evidence for complex formation between the xylans and some Group II cations, and in this Instance it seems quite unlikely that more than 2 hydroxyl groups per residue can be coordinated to the same metal ions. 

Evidence for Complex Formation between Component Proteins... 

Lavallee, R.J. Zimmt, M.B. Interaction between electrolyte and charge-transfer status Evidence for complex formation. J. Phys. Chem. 1994. 98, 4254-4260. 

In the reactions with hydroxylamine and its methyl derivative and with nitrous acid there is no evidence for complex formation, and six... 

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